Multistatic 3D Whole Body Millimeter-Wave Imaging for Explosives - - PowerPoint PPT Presentation

Carey Rappaport

ALERT Center of Excellence Northeastern University, Boston, MA

Multistatic 3D Whole Body Millimeter-Wave Imaging for Explosives Detection

IEEE Distinguished Lecture, Qualcomm, December 6, 2019

Outline § State of the art § Multistatic radar § Blade beam reflector § Elliptical toroidal reflector § Penetrable dielectric imaging § Experimental results

3

Mm-Wave Imager: Current State-of-the- Practice – L3 ProVision

§ Detects many types of materials based on shape (metallic and non-metallic): liquids, gels, plastics, metals, ceramics § Limitations

§ “Dead Spots” § No chemical info § Limited views § Poor penetration through leather and metallic clothing § No penetration through skin or into body cavities

4

State of the art

Current mm-wave scanners are based on monostatic radar:

• Presents specular reflection only –

no depth encoding

• Uses Fourier inversion – fast, but

not best for close imaging.

• Shows shapes of metallic objects,

but does not fully consider reverse imaging

• f weak

dielectrics (i.e. explosives). Dihedral Artifacts Non-spectral Dropouts

Sheen, D., McMakin, D., Hall, T., “Three-Dimensional Millimeter Wave Imaging for Concealed Weapon Detection,” IEEE T-MTT, 9/01

Monostatic / Multistatic Radar § Monostatic § Multi-monostatic § Bistatic § Multi-bistatic § Multistatic

Radar Focusing Resolution –Point Spread Function

Range resolution: ~ c / 2BW Cross range resolution: ~ r l / d Range r Aperture width d

Imaging with Mm-Wave Radar § Raster scanned focused point § Electronically scanned phased array § Synthetic aperture radar

Multi-Monostatic vs. Mulitstatic Mm-Wave Radar Imaging Example

• 0.2
• 0.1

0.1 0.2 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Multi monostatic SAR image setup

Multi-Monostatic: Dihedral images to a point

• 0.2
• 0.1

0.1 0.2 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Multistatic SAR image setup

Multistatic: Dihedral images to correct corner scatterer

9

Detection Regimes

§ Distant targets (10 m to >100 m),

§ Stand-off detection of hazards § Far enough away to minimize threat

§ Mid-range targets (3 to 10m)

§ Enhanced sensing discrimination § Not explicitly surrounding target

§ Intimately near targets (< 3 m)

§ Non-invasively examined § Mostly portal sensors

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Innocent Case Geometry

Full-Wave Modeling of Radar Scattering from Accurate Anatomic Geometries

Threat Case with 9 Pipe Bombs

www.nlm.nih.gov/research/visible/visible_human.html

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Snapshot of Waves Interacting with Scatterers

12

77 GHz TM Uniform Plane Wave Scattering from Torso with and without Pipes

Considerable interference from various scattering points on torso But variation across torso skin surface is slow Pipes further confuse scattering And variation is rapid

§ Custom designed elliptical torus reflector allows multiple overlapping beams for focused wide-angle illumination to speed data acquisition and image inclined body surfaces. § Multiple transmitters provide horizontal resolution and imaging of full 120 deg. of body. § Multistatic Tx and Rx array sensing avoids dihedral artifacts from body crevices and reduces non-specular drop-outs.

Overview & Technical Approach

Blade Beam antenna z axis (m) x axis (m) y axis (m) Normalized amplitude (dB)

Human body torso

True profile Estimated profile

Normalized amplitude (dB)

(1) 2D imaging (one slice)

(2) Stacked 2D images (slices)

(3) 3D surface generation (4) ATR algorithm and results display

Vertical (z- axis) motion

Operational Concept: Stack 2D Slices to Generate 3D Surface – Minimize Hardware, Simplify Calculation

15

System setup: Specially Designed Elliptical Parabolic Reflector Focuses to a Thin Slice on Body

Parabolic in azimuth

• Gives wide beam
• Parallel incident rays

Patent Pending on Novel Reflector Design

Elliptical in elevation

• Tight “Blade Focus”
• Illuminates narrow slice

z

Elliptical Torus Reflector – Surface of Revolution Allows Multiple Scanned Transmitters

First focal point (feed) Second focal point (target) Axis of revolution

Reflector View from Above for Two Feed Positions 0 and 45°

Tx position

Target (0.2x0.4 half elliptical cylinder)

Tx position Target 45o Circular Focal Arc

Second Focal Line

Second Focal Line

Torus Reflector Configured with Both Transmit and Receive Elements on Focal Arc, Facing Torus

Receiver Transmitter Imaging Target Toroidal Reflector

Aluminum Reflector Machined with CNC Milling Machine – 0.0001m Surface Tolerance

Back view, showing rough cuts for weight reduction § 4 Identical panels § 8 kg per panel § Elliptical vertical profile X circular arc horizontal profile

dB

0° 15° 30° 45°

Reflector / Cylinder Target Illumination for Scanned Transmitters --Simulation

Tx Position Reflector Illumination Target Illumination

Blade beam

Vertical motion

• Freq. band: 56-63 GHz

Range resolution: 25mm

Computed Illumination from Vertically Translating Toroidal Reflector

Multistatic Imaging with Torus Reflector – 20 deg. Inclined Metal Box, Half Receiver Arc

Ground Truth in Green Image from Modeled Data Image from Measured Data

SAR Reconstruction of Mm-Wave Radar Measurements

Radon / Inv. Radon processing Curved metallic torso surrogate with attached square pipe Original Reconstruction

Dielectric (Explosive) Slab on Skin Characterization Waves travel more slowly through dielectric:

§ Slab delays response from back surface (skin reflection), making primary image look farther away (L3 Provision, Rohde & Schwarz) Wideband, Time Domain, Impulse § Slab refracts focused rays, making response appear closer to sensor (Smiths) Frequency Domain -- CW

Dielectric Slab Dielectric Slab Focusing Aperture

Determine Thickness and Dielectric Constant

er =3

Amplitude (dB)

er = 3

Determining Slab Dielectric Constant with Wideband Imaging, Using Depth (Range) Response

Skin: e = 11.9 e0 + j 55.6 / ( 2 p f) Object 1 Object 2

1 cm 4 cm 2 cm

𝜁" 𝑭𝒕𝒖 = 1 + 𝑒*+,-. 𝑒/01

2

dobj ddelay

𝜁" 𝑭𝒕𝒖 = 1 + 3/4 2 = 49/16

Álvarez, Y., Gonzalez-Valdes, B., Martínez-Lorenzo, J., Las-Heras, F., & Rappaport, C., “SAR Imaging-Based Techniques for Low Permittivity Lossless Dielectric Bodies Characterization,” IEEE Ant. Prop. Mag., 4/2015, pp. 267 - 276.

US Patent 9,575,045, 2/15/2017, Rappaport and Martinez, “Signal Processing Methods and Systems for Explosive Detection and Identification Using Electromagnetic Radiation”

Metal Plate Skin Simulant with Small Affixed Explosive Simulant Bar

Penetrable affixed dielectric images as a depression

Metal Torso Simulant with Small Affixed Metal and Explosive Simulant Bars

Hallway Detector Paradox: Single Planar Array Requires Unrealistically Wide Aperture for Reasonable Resolution

Subject Array Position in Wavelengths (l = 0.5 cm)

• 30 GHz bandwidth,
• 60 GHz center frequency
• 0.5 cm X 0.5 cm resolution

100 200 300

Movement Direction

x axis, in m (movement direction)

y a x i s , i n m ( c r

• s

s

• m
• v

e m e n t d i r e c t i

• n

)

M

• v

e m e n t d i r e c t i

• n

Transmitters Receiving aperture Receiving aperture

Subject

z axis, in m (elevation)

Hallway, “On-the-Move” Person Scanning Concept – Imaging Subject’s Front and Back

Hallway Detector Solution: Dual Planar Arrays (or Apertures) Capture Non-Specular Scattering with Reasonable Resolution

Subjec t

100 200

Movement Direction

Combined image

• 6 dB
• 12 dB
• 18 dB

Incident waves Reflected waves Movement direction

Reflectivity amplitude, in dB

Receiving aperture Transmitters x axis, in m (movement direction)

Initial position Final position

y axis, in m (cross-movement direction) Transmitters

Provisional Application No. 61/912,630, “On the Move Millimeter Wave Interrogation System with a Hallway of Multiple Transmitters and Receivers,” Gonzalez, Rappaport, and Martinez.

Hallway Wideband Radar – Left Side Receiving Aperture Only

Conclusions

§ Extension of Blade Beam Reflector into Elliptical Torus for multiple overlapping high quality beams § Illumination and receiver focusing on narrow slice for fast computation § Fabrication, testing, optimization of wideband 60GHz multistatic radar § Novel reflector antenna, stacked 2D reconstruction, and fast inversion for real time processing § Minimal artifacts from dihedrals, full depth information and advanced visualization

This work supported by U.S. Dept. of Homeland Security, Award # 2008-ST-061-ED0001.

The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied of the Dept. of Homeland Security.